As a technique related to such an ultra-low temperature freezer, a door apparatus, for example, is described in Patent Literature (PTL) 1 for a cooling storage cabinet. With this door apparatus, when an outer door is closed, a cabinet-interior-end surface of a flange abuts an entry lip on an outer side of the cabinet via packing that serves as a seal member. It is to be noted here that in this door apparatus, the cabinet-interior-end abutment surface and an abutment surface of the packing are both flat.